1. Acids and Bases

2. Learning outcomes

3. Acids and Base effect on Litmus
Acid turns litmus red
Base turns litmus blue

4. Acids Sour taste Turn blue litmus RED (ABR) Neutralise bases
React with metals to produce Hydrogen

5. What do they all have in common?
Acids
Common lab acids
Hydrochloric acid: HCl
Sulphuric acid: H2SO4
Nitric acid: HNO3
Everyday acids
Ethanoic acid (Vinegar): CH3COOH
Carbonic acid (Fizzy drinks): H2CO3
Citric acid: C6H8O7
Dil. sulphuric acid in car batteries H2SO4
*(need to know 2 for exam)
What do they all have in common?

6.  They all contain Hydrogen.
Acids
 They all contain Hydrogen.
Classification of acids
Acids are classified as
Monobasic
Dibasic or
Tribasic
depending on the number of hydrogen atoms per molecule that are removed by reaction with a base

7. Acids
Donates
Example
Monobasic
Dibasic
Tribasic

8. Acids Donates Example Monobasic Dibasic Tribasic One H+ Two H+
Three H+

9. Acids Donates Example Monobasic Dibasic Tribasic One H+ HCl Two H+
H2SO4
Tribasic
Three H+
H3PO4

10. Bases Bitter taste Slippery feel Turn red litmus blue (BRB)
Neutralise acids
A base that dissolves in water is called an alkali.

11. What do most of these have in common?
Everyday bases
Milk of Magnesia neutralises stomach acid: Mg(OH)2
Sodium Hydroxide in oven cleaners: NaOH
Calcium Hydroxide in limewater: Ca(OH)2
Calcium carbonate: CaCO3
Soaps
* (need to know 2 for exam)
What do most of these have in common?

12. Defining Acids and bases Arrhenius vs Bronsted-Lowry

13. Arrhenius: Definition of Acids
An acid is:
a substance that dissociates in water to produce H+ ions.
HX  H+ + X-
HCl  H Cl-
H2SO4  2H+ + SO42-

14. Arrhenius: Strong and Weak Acids
Arrhenius’ defined some acids as strong and others as weak.
 A strong acid is one that fully breaks up (dissociate) in water to give hydrogen ions
= HA
= H3O+ + + - - + -
= A- + - + - + - + -

15. Arrhenius: Strong and Weak Acids
A weak acid only slightly dissociates in water to give hydrogen ions
= HA + -
= H3O+ + + + -
= A- - -

16. Summary of Arrhenius’ Acids
Strong/ Weak
Dissociation
Classification
Hydrochloric
Strong
HCl → H+ + Cl-
Monobasic
Nitric
HNO3 → H+ + NO3-
Sulfuric
H2SO4 → 2H+ + SO42-
Dibasic
Phosphoric
Weak
H3PO4 → 3H+ + PO43-
Tribasic
A strong acid is one that fully dissociates in water to give hydrogen ions
A weak acid only slightly dissociates in water to give hydrogen ions

17. Arrhenius: Definition of Bases
An base is:
a substance that dissociates in water to produce OH- ions (hydroxide ion).
XOH  X+ + OH-
NaOH  Na+ + OH-
Mg(OH)2  Mg2+ + 2OH-

18. Arrhenius: Strong and Weak Bases
 A strong base is one that fully dissociates in water to give hydroxide ions (OH-)
 A weak base is one that only partially dissociates in water to give hydroxide ions (OH-)

19. Summary of Arrhenius’ Bases
Strong/ Weak
Dissociation
Sodium Hydroxide
Strong
NaOH → Na+ + OH-
Magnesium Hydroxide
Weak
Mg(OH)2 → Mg2+ + 2OH-
Calcium Hydroxide
Ca(OH)2 → Ca2+ + 2OH-
A strong base is one that fully dissociates in water to give hydroxide ions (OH-)
A weak base only slightly dissociates in water to give hydroxide ions (OH-)

20. Which represents a weak acid dissolved in water?

21. Which is the strongest acid?

22. HW Show using a diagram how these would dissociate in water:
Strong base
Weak base

23. Problems with Arrhenius’ Theory of Acids and Bases
1. The H+ ion produced when an acid dissociates reacts with the water molecule to form the H3O+ (hydronium ion).
This is what exists in solution and not H+.
HCl + H2O → H3O+ + Cl-
2. His theory only holds for reactions occurring in water. No other solvents are included.

24. Formation of Hydronium Ions
An acid is a substance that dissociates in water to produce H+ ions. 1+ 1+ 1+ + H+
H2O
H3O+
hydrogen ion
water
hydronium ion
(a proton)

25. Formation of Hydronium Ions
An acid is a substance that dissociates in water to produce H+ ions.
HCl + H2O → H+ + Cl- + H2O
HCl + H2O → H3O+ + Cl-

26. Bronsted and Lowry (1923)
They continued on Arrhenius’ work and redefined Acid and Bases.

27. Bronsted and Lowry (1923) ACID = DONOR
 An acid is a substance that donates H+ ions (proton) in solution .
ACID = DONOR
A base is a substance that accepts H+ ions (proton) in solution

28. Bronsted and Lowry (1923) HCl + H2O → H3O+ + Cl-
Consider:
HCl + H2O → H3O+ + Cl-
The molecule of HCl has given its H+ ion to water. Since HCl has donated its proton it is called an acid.
The molecule of H2O has accepted the H+ ion from HCl and is therefore a proton acceptor - a base.

29. Bronsted and Lowry (1923) A strong acid is a good proton donor
A weak acid is a poor proton donor
A strong base is a good proton acceptor
A weak base is a poor proton acceptor

30. Advantages of Bronsted-Lowry Theory over Arrhenius’s.
This theory does not require water as a solvent.
It has a broader range of species that can be defined as an acid and a base which may not have been classified under the Arrhenius theory.
Conditions:
The B/L theory will only work if there is an acid present to donate a proton but also there must be something to accept this proton.
Similarily a base will only accept an H+ion if there is an acid there to donate it.

31. HCl + NH3 → NH4+ + Cl- What am i? Donates Proton (Acid) Accepts a
Proton (Base)

32. NH3 + H2O → NH4+ + OH- What am i?
Here the H2O molecule dissociates into H+ and OH-
The NH3 accepts the H+ ion to give NH4+ and so under Bronstead- Lowry rules is a base.
The water donates the proton and is therefore the acid.

33. Water can act as an acid and a base??
HCl + H2O → H3O+ + Cl- NH3 + H2O → NH4+ + OH-

34. Amphoteric 
A substance that can act as an acid and a base is called an amphoteric substance.
Water can act as either an acid or a base....

35. Conjugate Acid-Base Pairs
Conjugate pair:
Two substances which differ by a H+
An acid changes into its conjugate base when it donates a H+.
HCN  CN-
A base changes into its conjugate acid when it accepts a H+.
HCO3-  H2CO3

36. Exercise #1 HCN ----------- CN- HClO3 ----------- ClO3-
What are the conjugate bases of each of the following Bronsted- Lowry Acids:
HCN  CN-
HClO  ClO3-
NH  NH3
H2S  HS-
HF  F-
H2O  HO-
H2SO  HSO4-

37. Exercise #2 HCO3- ----------- H2CO3 NH2- ----------- NH3
What are the conjugate acids of each of the following Bronsted- Lowry Bases:
HCO  H2CO3
NH  NH3
Cl  HCl
SO  HSO4-
HF  H2F+
NH  NH4+

38. Conjugate Acid-Base Pairs
Accepts/adds a H+
H2SO4 + NH3 ↔ NH4+ + HSO4-
H2SO4 donates a proton and so is an B/L acid. Its conjugate base is HSO4- as it differs by one proton.
NH3 accepts a proton and so is a B/L base. Its conjugate acid is NH4+ as it differs by one proton.
Donates/ removes a H+
Conjugate acid-base pair

39. Conjugate Acid-Base Pairs↔
This symbol means a reaction can take place in both directions
CH3COOH + H2O ↔ CH3COO- + H3O+
Conjugate acid-base pair
Conjugate acid-base pair

40. Conjugate Acid-Base Pairs
For the forward reaction:
CH3COOH + H2O → CH3COO- + H3O+
B/L Acid B/L Base
For the reverse reaction:
CH3COOH + H2O ← CH3COO- + H3O+
B/L Base B/L Acid

41. Exercise HCl + OH- ↔ Cl- + H2O H2O + H2SO4 ↔ HSO4- + H3O+
Label the acids, bases and conjugate acid-base pairs present in each of these equations:
HCl + OH- ↔ Cl- + H2O
H2O + H2SO4 ↔ HSO4- + H3O+

42. Exercise NH3 + H2O ↔ NH4+ + OH- HNO2 + H2O ↔ NO2- + H3O+
Label the acids, bases and conjugate acid-base pairs present in each of these equations:
NH3 + H2O ↔ NH4+ + OH-
HNO2 + H2O ↔ NO2- + H3O+

43. Label the acid /bases and conjugate acid/bases
Answer

44. Label the acid /bases and conjugate acid/bases
Answer

45. Label the acid /bases and conjugate acid/bases
Answer

46. Label the acid /bases and conjugate acid/bases
Answer

47. Label the acid /bases and conjugate acid/bases
Answer

48. Strength of Conjugate acids/Bases
Strong acid  Weak conjugate base
Weak acid  Strong conjugate base
Same applied for bases

49. Neutralisation Acid + Base  Salt + Water
Neutralisation is a reaction between an acid and a base to form a salt and water
HCl + NaOH  NaCl + H20
The metal from the base replaces the H+ in the acid
Acid + Base  Salt + Water

50. Everyday examples of Neutralisation
Sodium Hydrogen Carbonate NaHCO3 in Alka Seltza is taken to neutralise excess HCl in the stomach
Lime (Calcium hydroxide) is added to soil or water to neutralise it
Toothpaste contains a base to neutralise the acids in food